The invention relates to cyclonic separating apparatus and to a method of separating dirt from dirt-laden air. Particularly, but not exclusively, the invention relates to cyclonic separating apparatus suitable for use in a vacuum cleaner.
Cyclonic separating apparatus is well known. In such apparatus, the dirt-laden air is introduced to the interior of a cyclone body in a tangential manner. The air follows a helical path around the interior surface of the cyclone body so that centrifugal forces act on the entrained dirt. At the bottom of the cyclone body, the airflow reverses its direction of travel parallel to the axis of the cyclone body and the dirt is separated from the main airflow. The separated dirt collects at the bottom of the cyclone body whilst the cleaned air exits the apparatus via a centrally located outlet at the top of the cyclone body. Examples of the application of this type of separating apparatus to domestic vacuum cleaners are shown in EP 0 042 723, U.S. Pat. Nos. 5,160,356 and 5,078,761.
One disadvantage of this type of arrangement is that, as the amount of collected dirt increases, the risk of that collected dirt being re-entrained into the airflow increases. Some attempts have been made to alleviate this problem by providing a dirt collection chamber, separate from the cyclone body, into which the collected dirt is transferred and in which it is allowed to accumulate. The cylinder vacuum cleaner manufactured by Electrolux and marketed under the name xe2x80x9cCYCLONE POWER BAGLESS HOME CLEANING SYSTEMxe2x80x9d (Model Number Z58102T) incorporates such a feature. A similar arrangement is shown in TWO 9611047. In theory, the collected dirt is kept separate from the main airflow which reduces the risk of re-entrainment so that larger volumes of separated dirt can be collected before the apparatus requires to be emptied. However, because the dirt-collection chamber is closed in all areas except at the inlet thereto, any air which enters the dirt-collection chamber is forced to follow a circuitous path and must exit the dirt-collection chamber via the inlet. This leads to a not insignificant amount of turbulence inside the dirt-collection chamber which can lead to previously separated dirt being carried back into the mainstream airflow by the returning air. Another disadvantage of the turbulent conditions existing within the closed dirt-collection chamber is that the separated dirt is carried to many different parts of the dirt-collection chamber. This makes the emptying of the dirt-collection chamber more complicated especially if it is desired to make use of emptying means which allow the user to avoid being exposed to the contents of the dirt-collection chamber.
It is an object of the present invention to provide cyclonic separating apparatus in which the risk of re-entrainment of separated dirt is reduced. It is a further object to provide cyclonic separating apparatus in which the capacity of the apparatus to collect dirt is improved. It is a still further object to provide cyclonic separating apparatus in which the risk of re-entrainment of separated dirt is reduced and the capacity of the apparatus to collect dirt is simultaneously increased. It is a still further object of the invention to provide cyclonic separating apparatus which can be easily and conveniently emptied in a manner which allows the user to avoid being exposed to the dirt collected in the dirt-collection chamber. It is a still further object of the invention to provide a method of separating dirt from dirt-laden air in which the risk of re-entrainment of separated dirt is reduced.
The invention provides cyclonic separating apparatus as set out in claim 1. The invention also provides a method of separating dirt from dirt-laden air as set out in claim 21. Preferred and advantageous features are set out in the subsidiary claims.
The provision of an air return duct communicating with the collecting portion of the dirt-collection chamber and with the interior of the cyclone body provides a separate exit path via which air entering the dirt-collection chamber can return to the cyclone body. This has a number of advantages. Firstly, the airflow within the dirt-collecting chamber is less turbulent so the risk of re-entrainment of dust is reduced. Also, since little or no air is reintroduced to the main airflow in the cyclone body via the entry portion, there is less disturbance to the main airflow. Thirdly, by allowing a small amount of air to flow through the dirt-collection chamber, the separated dirt and fibers can be encouraged to collect in a defined area of the collecting portion from which the separated dirt and fibers can easily be emptied, if required without exposing the user to the collected dirt.
It is preferred that the second end of the air return duct approaches the interior of the cyclone body in a direction which is inclined at an acute angle to the direction of flow within the cyclone body at the point of communication therewith. This is advantageous because, in use, the flow of the main airflow past the second end of the air return duct causes, by the venturi effect, air to be drawn out of the dirt-collecting chamber and into the interior of the cyclone body. This in turn helps to smooth the airflow path through the dirt-collecting chamber.